Plant oil, largely in the form of triacylglycerol (TAG), is attractive as a renewable resource to supplant or replace petroleum as a source of many compounds. Unlike most commercial oilseeds containing oil comprised predominantly of just five main fatty acids, namely palmitic (C16:0), stearic (C18:0), oleic (C18:1), linoleic (C18:2) and α-linolenic (C18:3) acids, many exotic plant species have been found to contain high levels of unusual fatty acids, such as hydroxy, epoxy, and acetylenic fatty acids (van de Loo, et al., 1993). For example, an epoxy fatty acid, known as vernolic acid (cis-12-epoxyoctadeca-cis-9-enoic acid), can accumulate at levels up to 50-90% of the total fatty acids found in the seeds of Vernonia galamensis, Euphorbia lagascae, Stokesia laevis, Crepis palaestina, and Bernardia pulchella (Bafor, et al., 1993; Pascual and Correal, 1992; Perdue, 1989; Spitzer, et al., 1996; Thompson, et al., 1994). These unusual fatty acids have unique properties that make them valuable as renewable raw materials for the chemical industry, and, in fact, many of these unusual fatty acids are used in making dyes, paints, coatings, adhesives, composites, plastics, and a variety of other products (Jaworski and Cahoon, 2003). However, despite the value of these unusual fatty acids, the commercial production of the plants used to produce them has been significantly hampered due to the poor agronomic properties of those plants, such as low seed yields and low seed retention, which thus make the plants agronomically unsuited for industrial-scale growth and processing.
Metabolic engineering of oilseeds provides a platform for the production of these unusual fatty acids. However, recent efforts to express genes driving the synthesis of unusual fatty acids in commercial oil crops have been generally met with only limited success, with much lower amounts of the desired fatty acid accumulating in the oils of transgenic plants as compared with the native plant species (Burgal, et al., 2008; Cahoon, et al., 2007; Jaworski and Cahoon, 2003; Singh, et al., 2005; Thelen and Ohlrogge, 2002). Indeed, the transgenes used in these previous attempts to synthesize unusual fatty acids have been mainly divergent members of the Δ12-oleic acid desaturase gene family, which encode alternative enzymatic functions, such as epoxidation, hydroxylation, acetylenation, and conjugation, rather than the function of the typical fatty acid desaturase that catalyzes the introduction of a cis-Δ12 double bond in oleic acid (C18:1) to form linoleic acid (C18:2). As such, it is clear from these previous reports that for developing engineered oilseeds that accumulate higher levels of industrially-important unusual fatty acids, additional genes are needed, including genes responsible for the efficient and selective flux of unusual fatty acids from the site of synthesis on phospho lipids to storage in TAGs.